Regeneration of alkaline treating agents



uji ih-J I June-4, 1957 L EZL 2,794,769

' Sour Disulfides REGENERATION 0F ALKALINE TREATING ACENTS Filed'Mey 9,. 1955 a Sour Aqueous NOOH Hydrocarbons A 9 "1 1 y QJ Hydrocarbons-f Removu' 3 RSI-I Removal u 23 l4 Regeneration 1/ Elecfmlyfig 7 with Epoxide Regeneration 4 V f .32 l2 Electro'yhc Disulfide Regeneration v Removal M Y Regeneroted Disolfide NoQH Removal 1 INVBVTOR.

JAMES L. JEZ'L ATTO NEY REGENERATION OF ALKALINE TREATING AGENTS James L. Jezl, Swarthmore, Pa., assignmto Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application May 9, 1955, Serial No. 507,105

3 Claims. (Cl. 19632) This invention relates to the regeneration of alkaline treating agents containing alkali metal sulfides.

It is known in the art to electrolytically regenerate alkaline treating agents which have been used in the treatment of mineral oil fractions. Such regeneration may be accomplished by passing the used caustic soda through an electrolytic cell to which electric current is supplied at a suitable voltage. The water in the caustic soda is electrolyzed, oxygen and hydrogen being thereby formed. The oxygen reacts with the sodium mercaptides to form disulfides, or with sodium sulfide to form free sulfur or other products. The disulfides can be subsequently separated from the caustic soda, for example by extraction with naphtha.

Electrolytic regeneration provides an advantageous reduction in mercaptide and sulfide content of caustic, but has been found to produce unsatisfactory results when sulfides are present in the caustic which is to be regenerated, in that the sulfides form not only free sulfur but undesirable products such as sulfites, sulfates, etc. which may ultimately precipitate from the caustic and cause, in addition to neutralization of the caustic and other undesirable etfects, severe deposition difficulties in the electrolytic cell and elsewhere in the caustic circulation system.

In order to avoid this difficulty, it has been proposed previously to remove hydrogen sulfide from sour hydrocarbons prior to contacting the latter with the caustic which is to be regenerated electrolytically. However, this method, as practiced in the prior art, resulted in a disposal problem with regard to the hydrogen sulfide which was removed.

According to the present invention, a novel process is provided whereby hydrogen sulfide contained in sour hydrocarbons to be treated is utilized to particular advantage. This is accomplished by converting the hydrogen sulfide to alkali metal sulfide, then reacting the sulfide with an epoxide to form organic sulfur compounds in the alkaline treating agent.

According to one embodiment of this invention, the alkaline treating agent is then used to remove mercaptans from substantially H2S-free sour hydrocarbons, the resulting treating agent then being regenerated electrolytically. This process is particularly advantageous in that the reaction products of epoxide with alkali metal sulfide have a solutizing effect in the subsequent removal of mercaptans, the latter being rendered more soluble in the caustic by virtue of the presence of the reaction products; and also in that the caustic which is electrolytically regenerated is substantially free of alkali metal sulfide, so that disadvantageous products from alkali metal sulfides are not obtained in the electrolytic regeneration.

According to another embodiment of the invention, an alkaline treating agent containing both alkali metal sulfide and alkali metal mercaptides is first contacted with an epoxide to react the latter with alkali metal sulfide, and the resulting treating agent is electrolytically regenerated to convert mercaptides to disulfides.

In the epoxide regeneration of treating agents containatent' ing alkali metal sulfides and mercaptides, the following represent the principal reactions, ethylene oxide being the epoxide for purpose of illustration:

N828 CHZCHSI H NaSOHiCHzOH (hydroxyethyl mercaptide)v NaOH NBSCHzCHzOH CHzCHz H2O HOCHzCHzS CHIOH20H (diethanol sulfide) NaOH RSNa CHzCHz H5O RS CHzOHrOH (hydroxyethyl thloether) NaOH Reaction No. 1 proceeds considerably more readily than Reactions No. 2 and 3. Reaction No. 2 probably proceeds slightly more readily than Reaction No. 3. The use of small amounts of epoxide, short contacting times and low temperatures tends to result in Reaction No. l proceeding to the substantial exclusion of the other two, and Reaction No. 2 proceeding more extensively than Reaction No. 3.

In the electrolytic regeneration of treating agents containing alkali metal mercaptides and possibly hydroxy alkyl mercaptides formed in preceding epoxide regeneration, the following are the principal reactions:

Thus the products obtained include dihydrocarbon disulfides, diethanol disulfide, and monoethanol monohydrocarbon disulfides. The dihydrocarbon disulfides are the least soluble in the caustic and therefore the most readily recoverable therefrom, e. g. by extraction with a hydrocarbon solvent. The diethanol disulfide is the most soluble in the caustic and can advantageously be left therein to function as a solutizer in subsequent use of the caustic to remove mercaptans from hydrocarbons. The monoethanol monohydrocarbon disulfides are intermediate in solubility; they as well as the dihydrocarbon disulfides can be removed from the caustic, or they can be left in the caustic if desired.

In the process of the invention, hydrogen sulfide is converted to useful sulfur compounds such as diethanol sulfide, diethanol disulfide, monoethanol monohydrocarbon disulfides, etc. As previously indicated, these compounds can advantageously be used as solutizers, i. e. to increase mercaptan solubility in caustic upon use of the latter to remove mercaptans from hydrocarbons. These compounds may also be used to advantage as mineral oil additives, e. g. as coupling agents in emulsifiable mineral oil compositions containing an emulsifying agent, or as extreme pressure additives in lubricants, etc.

The electrolytic regeneration following the epoxide treatment can be conducted according to any of the known procedures for such regeneration. Thus, for example, the procedures disclosed in United States Patent No. 2,654,706 issued October 6, 1953, to Peter J. Gaylor can be employed. Any of the known methods of separating disulfides from the regenerated treating agent can be employed.

The epoxide regeneration is performed by contacting the used treating agent with an epoxide capable of reacting with the sulfides and mercaptides in the treating agent. The temperature may be ordinary room temperature or higher or lower temperatures, e. g. 30 F.

to 300 F. Preferred epoxides are those having the formula:

' L f gi A61 where R is selected from the group consisting of hydrogen, halogen radicals, hydrocarbon radicals having 1 to 5 carbon atoms, phenoxyalkyl radicals having 7 to 10 carbon atoms, alkoxyalkyl radicals having 2 to 10 carbon atoms, and

where R is selected from the group consisting of hydrogen and alkyl radicals having 1 to 2 carbon atoms. Examples of suitable epoxides are ethylene oxide, prov employed per mole of sulfide.

pylene oxide, butylene oxide, styrene oxide, phenoxy propylene oxide, butoxy propylene oxide, epichlorohydrin, butadiene oxide, etc.

The alkaline treating agent which is regenerated according to the invention can have been used to refine any of various petroleum materials, e. g. crude oil, reduced crude, kerosene, spirits, gasoline, gas oil, furnace oil, diesel'fuel, jet fuel, lubricating oil, natural gas, refinery gas, liquefied petroleum gases, etc., and may contain materials such as phenolates and naphthenates in addition to mercaptides or inorganic sulfides.

The invention will be further described with reference to the attached drawing, which is a flowsheet of a process for regenerating alkaline treating agents according .to the invention.

Sour hydrocarbons, e. g. straight run gasoline containing mercaptans and hydrogen sulfide, are introduced into hydrogen sulfide removal zone 10 where they are contacted with an aqueous solution of caustic soda under conditions producing removal of hydrogen sulfide, the removal of mercaptans being minimized. It is within the ability of a person skilled in the art to select the conditions, such as amount and strength of caustic etc., to obtain this result, the reaction of sodium hydroxide with hydrogen sulfide'occurring more readily than that of sodium hydroxide with mercaptans.

The used caustic containing sodium sulfide is contacted in zone 11 with an epoxide, e. g. ethylene oxide, the contacting being performed for example at room temperature with agitation followed by standing for one hour. Preferably, l to 5 moles of epoxide per mole of alkali metal sulfide are employed. If substantially complete removal of alkali metal sulfide is desired, the amount is preferably at least 1.5 moles of epoxide per mole of alkali metal sulfide. If conversion of inorganic sulfide to dialkanol sulfide is desired, rather than merely to hydroxy alkyl mercaptide, preferably at least 3 moles of epoxide per mole of alkali'metal sulfide are employed. The above proportions apply generally to epoxides having only one epoxy group; epoxides having more than one epoxy group can be used in correspondingly lesser amounts. The amount of epoxide to be employed to achieve a given purpose may vary depending on the other conditions; e. g. short contact times, low temperatures etc. are factors which, like small amounts of epoxide, tend to limit the extent of reaction of epoxide with constituents of the caustic.

The regenerated caustic is passed through lines 16 and 1 7 and used in zone 13 to treat the sour hydrocarbons from which hydrogen sulfide was removedin.

zone 10. This treatment will be further described subsequently.

Instead of removing mainly only H28 in zone 10, removal of H28 and partial removal of mercaptans can be efiected in zone 10, and caustic containing sodium sulfide and mercaptide recycled through lines 21 and 18 to contact additional sour hydrocarbons containing hydrogen sulfide and mercaptans. The presence of mercaptides in the caustic greatly inhibits removal of mercaptans from the sour hydrocarbons by the caustic, but highly effective removal of hydrogen sulfide. can be obtained in spite of the presence of sodium sulfide in the caustic. A drag stream from the circulating caustic is introduced through line 20 into epoxide regeneration zone 11 wherein it is contacted with an epoxide, e. g. ethylene oxide. Preferably 1 to 5 moles of epoxide are More preferably, at least 1.5 moles of epoxide per mole of sulfide are used, and sulfide is substantially completely converted, part .probably being converted to hydroxyethyl mercaptide and part to diethanol sulfide. Sodium mercaptides are only partially converted to hydroxythioethers. If minimization of mercaptide reaction with epoxide is desired, preferably not more than 2, and more preferably not more than 1.5 moles of epoxide per mole of alkali metal sulfide are employed. On the other hand, if conversion of alkali metal disulfide to dialkanol sulfide is desired,

. erated in zone 12 to convert remaining sodium mercaptides to disulfides, the latter being removed in zone 20. The caustic is then passed through lines 31 and .17 into zone 13.

Instead of returning caustic to zone 10 through line 21 the caustic can be regenerated in zone 11' and returned through lines 16, 23 and 18 to zone 10, a drag stream 32.being taken for electrolytic regeneration.

The caustic introduced into zone 13 through line 17 may contain dialkanol sulfide, dialkanol disulfide, hydrocarbon disulfides, monohydroxy disulfides, or thioethers, or mixtures thereof, depending on the previous treatment of the caustic. Various of these materials act as solutizers to increase the solubility of mercaptans in the caustic during the treating in zone 13. Caustic containing sodium mercaptides is passed through zone 13 to zone 14 where it is electrolytically regenerated to convert mercaptides to disulfides, the latter being removed in disulfide removal zone 15. Other organic constituents of the caustic may be removed simultaneously, or separately by means not shown. The caustic may be used to contact additional hydrocarbons containing H28 or mercaptans or both. Thus, for example, the caustic can be recycled as often as practicable either to zone It through line 32 or to zone 13 through means not shown, etc.

In another embodiment, instead of introducing the treated hydrocarbons from zone 10 through line 25 into zone 13, the treated hydrocarbons can be withdrawn as a product through line 26, and a different sour hydrocarbon charge can be introduced through line 27 into zone 13. In this embodiment, the charge to zone It canbe, for example, an essentially mercaptan-free, HzS-containing hydrocarbon fraction, and the charge to zone 13 an essentially HzS-free, mercaptan-containing fraction.

The following examples illustrate the invention:

Example I mil.

to stand for an hour. The resulting caustic contained zero mg. of sodium sufide sulfur per liter and 6,500 mg. of mercaptide sulfur per liter. These sulfide and mercaptide contents were determined by electrometric titration with silver nitrate.

The caustic partially regenerated by epoxide treatment can be further regenerated electrolytically to reduce the mercaptide content, with highly satisfactory results and freedom from undesirable efiects which would arise if the electrolytic regeneration were performed in the presence of sodium sulfide. In such operation, electrolytic regeneration is used to convert at least part of the mercaptides, thus eliminating the cost of chemical reagents for that portion of the regeneration, and regeneration by means of an epoxide is employed for that part of the regeneration where the presence of inorganic sulfides would cause difficulties in electrolytic regeneration.

Example ll Aqueous caustic soda which had been used to treat gasoline for H28 and mercaptan removal, and which contained 2960 mg. (as sulfur) of sodium sulfide per liter and 2450 mg. (as sulfur) of sodium mercaptide per liter, was regenerated by contacting with 2 parts by volume of propylene oxide per 100 parts of caustic, at 32 F. with agitation and allowed to stand for 30 minutes. The resulting caustic contained zero mg. of sodium sulfide sulfur per liter and 2300 mg. of sodium mercaptide sulfur per liter; some of the latter is probably sodium hydroxy alkyl mercaptide formed by reaction of propylene oxide with sodium sulfide. After standing for 60 more minutes, at which time the system had reached equilibrium, the mercaptide sulfur content was further reduced to 1295 mg. per liter. The more highly selective sodium sulfide conversion obtained in 30 minutes indicates that it is possible, by use of smaller amounts of epoxide, to favor the selective conversion. In this example, about 3.2 moles of propylene oxide per mole of original sodium sulfide were employed, whereas 1.5 to 3 moles would have produced a more selective sodium sulfide conversion. It is also possible to remove excess epoxide from the caustic, e. g. by nitrogen blowing or solvent extraction, before equilibrium is reached, thereby favoring the selective conversion of sodium sulfide. The partially regenerated caustic can be further regenerated electrolytically to reduce the mercaptide content.

In the process according to the invention, complete conversion of sulfides and mercaptides by any step or combination of steps is not required, since an alkaline treating agent can often be made satisfactory for re-use by only partial conversion. Hower, complete or substantially complete conversion is within the scope of the invention. In any event, the extent of regeneration necessary for satisfactory re-use is often such that regeneration in multiple steps according to the invention is desirable.

In the preceding description, electrolytic regeneration has been disclosed with reference to electrolysis in the presence of the used caustic soda which is to be regenerated. Electrolytic regeneration as contemplated herein also includes introduction of freshly prepared electrolytic oxygen into the used caustic soda, the electrolysis zone and the regeneration zone being separate but the oxygen from the electrolysis zone being introduced into the regenerating zone directly after its formation.

The invention claimed is:

1. Process for refining petroleum which comprises: contacting an Has-containing petroleum fraction with aqueous alkali metal hydroxide; contacting the resulting aqueous solution containing alkali metal sulfide with an epoxide, thereby to react epoxide with alkali metal sulfide and produce conversion products having a solutizing effect on mercaptans; contacting an HzS-free, mercaptancontaining petroleum fraction with the epoxide-treated aqueous solution; electrolytically regenerating the resulting mercaptide-containing solution, thereby to convert mercaptides to disulfides; and then contacting additional Has-containing petroleum fraction with the electrolytically regenerated solution.

2. Process according to claim 1 wherein a petroleum fraction containing both H28 and mercaptans is the firstnamed fraction, and the same fraction after removal of H28 in the first-named contacting is the second-named fraction.

3. Process for refining petroleum fractions which comprises: contacting a petroleum fraction containing hydrogen sulfide and mercaptans With an aqueous solution of an alkali metal hydroxide; contacting the resulting solution containing alkali metal sulfide and mercaptides with an epoxide, thereby to react said epoxide with said alkali metal sulfide and produce conversion products having a solutizing effect on mercaptans; electrolytically regenerating the resulting solution containing alkali metal mercaptides, thereby to convert mercaptides to disulfides; and then contacting additional petroleum fraction containing hydrogen sulfide and mercaptanas with the electrolytically regenerated solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,805,444 Wilson May 12,1931

2,575,989 Arundale et al. Nov. 20, 1951 2,654,706 Gaylor Oct. 6, 1953 FOREIGN PATENTS 492,789 Great Britain Sept. 27, 1938 

1. PROCESS FOR REFINING PETROLEUM WHICH COMPRISES: CONTACTING AN H2S-CONTAINING PETROLEUM FRACTION WITH AQUEOUS ALKALI METAL HYDROXIDES; CONTACTING THE RESULTING AQUEOUS SOLUTION CONTAINING ALKALI METAL SULFIDE WITH AN EPOXIDE, THEREBY TO REACT EPOXIDE WITH ALKALI METAL SULFIDE AND PRODUCE CONVERSION PRODUCTS HAVING A SOLUTIZING EFFECT ON MERCAPTANS; CONTACTING AN H2S-FREE, MERCAPTANCONTAINING PETROLEUM FRACTION WITH THE EPOXIDE-TREATED AQUEOUS SOLUTION; ELECTROLYTICALLY REGENERATING THE RESULTING MERCAPTIDE-CONTAINING SOLUTION, THEREBY TO CONVERT MERCAPTIDES TO DISULFIDES; AND THEN CONTACTING ADDITIONAL H2S-CONTAINING PETROLEUM FRACTION WITH THE ELECTROLYTICCALLY REGENERATED SOLUTION. 